Sensitive electronic devices, such as piezoelectric devices typically require mounting in a hollow cavity within a ceramic/metal package. Such a package may include a ceramic/metal base or substrate being sealed with a lid, can, or shield. A common problem for sensitive electronic devices such as piezoelectric devices is providing an inert environment within the package. Another common problem is providing metal leads through a sealed ceramic package to connect with the internal device, and providing these leads and sealing the package while effectively preventing leaks due to thermal or mechanical stresses.
It is often the case where the ceramic and metal materials making up a packaging device have different coefficients of thermal expansion. This mismatch induces mechanical stresses as the part is exposed to different temperatures which occasionally results in leaks due to microcracking of the ceramic. In addition, external mechanical stresses may also contribute to microcracking.
Two main packaging schemes have been used for mounting piezoelectric devices. In a first scheme a piezoelectric element is suspended by a plurality of metal leads which extend through a glass plug in a substantially metal container. Although reliable, these packages, are not easily integrated into automated assembly production lines. In a second scheme a piezoelectric element is adhesively mounted to metal traces extending through a ceramic base. The base is subsequently sealed with a ceramic or metal lid by means of a metal or glass seal. Although this type of package is readily automatable, the ceramic base is expensive due to the multiple layers of preformed ceramic green sheet, and the many processing steps, typically needed to produce such a base.
A significant portion of the cost of a piezoelectric device is in its packaging. Previously, the packaging used for piezoelectric devices was typically ceramic packaging which has demonstrated good production yields. However, the ceramic structures themselves, though effective, are complicated and have a high inherent manufacturing cost. Cost reduction can be achieved if the packaging for piezoelectric devices can be simplified to allow ease of handling and automation.
There is a need for an improved package that: is low cost; minimizes the number of processing steps and separate packaging components; is robust under automation processes; is robust under mechanical shocks and environmental testing; and minimizes problems from differing thermal expansion coefficients between ceramic and metal packaging materials.
Accordingly, a robust, low cost, automatable, easily manufacturable package for a piezoelectric device which substantially eliminates leaks due to thermal stress cracks between a ceramic (or glass)/metal interface would be considered an improvement over the art.